Can anyone help me to solve a problem. If the weight of the molded component varies from piece to piece what correction is to be done?

is every piece is complate filled if it ok
then check every piece core and cv profile

Normally,two reasons, first injection pressure is not stable, there are some problems in hydraulic system, second, head of injection screw were weared, led to plastic melt leakage

The weight variation results in short filled components

I have mentioned this in other posts; the best practice is to apply scientific molding methods, a robust DOE, to your problem. This problem sounds like the process has not been properly defined or you have discovered a press deficiency such as a bad ring preventing the press from holding pressure. however, there are lots of other causes and without going over a painfully long and boring list you can solve this by conducting a proper scientific processing study. This should reveal the root cause. or if you prefer we can throw darts at this... which is, of course, great fun :)

first of all what is the raw material , check the cushion variation , if not consistent thn ur screw ring plunger is not ok , open the head and check & if need replace it , check & set back press.(bt not in case of GF mat) , this shud solve ur prob.

Material is PP.It is true that the injection pressure is not stable It starts at 650tons and goes down to 520 and stops during injection

by the way ,which plastic product do you process?

hi,
it sounds to me like a temperature problem.
either you are over heating the barrel or under cooling the mold.
at first the excess heat gives you material which is less compressed but better flow reducing both the injection pressure and the weight. bu the end you get the material so hot it is unable to eject the air out of the mold and you get a short shot.
do you control the barrel temp effectively or are you running on time percentages?
is your mold properly cooled? can you take a thermal image right after ejection of a short part compared to a good heavy part and compare them?
Daniel

This problem could have many reasons but 2 main check could be done
The first one check the injection machine valve
The second check that the injection machine size is enough for your product and if the injection machine plates does not open during the injection process.
Give status and results of these check

Ed is correct. The list of possible causes is very long. Machine/tooling issues, incorrect process set points, material lot variation, etc.
You will need to do all the scientific studies to determine root cause.
They are all public knowledge now, so you can get them online, but without an experienced person, you will get erroneous data and you will be lead down the wrong path, which can get expensive.

Ed is correct. If your machine has process control limits first thing is set you transfer point and cushion alarm. If these are being set off you should take the time and measure the wear on your check valve. Make sure your flights are not worn and your barrel is good.

On any new tool weight is the important to make sure the part is consistence. This is the best way to ensure your process is stable. It is something in the mechanical end inside the barrel.

What is the total weight of your Shot compared to the Maximum Barrel capacity ? Are you anywhere near the Barrel capacity ? Does your tool have adequate venting in the short shot area ? As previously mentioned, you may have an issue with a worn screw or possibly a cracked Check Ring.

Most of points has been highlighted..
My suggestion is check the mold 1st before going to press.
1. Check gate hole size, gate pin height (if any)
2. Check heater rating, if you are using zoned heaters, make sure you are getting the heaters from same source.
3. Check mold manifold is balanced, poorly designed may give a lot of problem.
4. Check mold manifold heaters rating.
5. Check mold cooling channels.
6. If the mold is new poorly drilled cooling channels may give problem too, such as choking, cooling plugs are not in place, etc.
7. Material flow channels must have mirror finishing to avoid any flow issue.
As above it has been mentioned there can be many reasons for mold is not balanced. I have attempted to mention few..